Aqueous-based pesticide formulations are increasingly popular due to their improved profile for mammalian toxicity and ecological effects, as well as reduced costs, compared to formulations utilizing an organic solvent as diluent. Unfortunately, introduction of even a small amount of water into a pesticide composition increases the potential for corrosion of metal surfaces of equipment used in manufacturing, storage, transportation or packaging of the product These corrosion characteristics may result in increased equipment maintenance costs or equipment failure.
The use of additives to reduce corrosion in pesticide compositions is known in the art However, the additives and applications disclosed are very specific in nature. For example, U.S. Pat. No. 2,788,307 discloses use of Na2S2O3 to reduce tinplate corrosion in contact with solvent-based lindane or DDT formulations. U.S. Pat. No. 2,630,380 discloses aryloxy polyethylene glycol compounds as inhibitors of corrosion in formulations based on 2,4-dinitro-6-alkylphenols. Use of bis(m-methylphenyl)phosphate to prevent iron corrosion in the presence of S-methyl-N-[(methylcarbamoyl)oxy]thioacetimidate is disclosed in JP 56034562. JP 2000034201 discloses compositions containing silica for preventing corrosion of containers by aqueous aerosols of pyrethroid insecticides. U.S. Pat. No. 5,061,698 discloses compositions based on boric acid with utility as corrosion inhibitors. U.S. Pat. No. 5,032,318 discloses C13-C14 alkylamine salts of N-acylsarcosine as corrosion inhibitiors for aerosols in tinplated steel cans. U.S. Pat. No. 5,118,444 discloses use of a specific class of amine oxides to reduce corrosion in aqueous pesticide compositions. The potential for corrosion in aqueous-based formulations is increased when the formulation is acidic in pH. There are a number of important pesticide active ingredients that contain an acid moiety in their structure and an aqueous-based formulation of these products may have an acidic pH. There may be other reasons for the pH of a pesticide formulation to be maintained at an acidic level, such as improved chemical stability for the active ingredient or improved physical stability for the product on storage. The presence of dissolved salts such as ionic chlorides or pesticide active ingredients present in salt or metal complex form may also accelerate corrosion of metal surfaces.
Surprisingly, it has been found that certain nitrate salt additives significantly reduce the corrosion properties of aqueous-based pesticide formulations, even with acidic pH levels and in the presence of a salt.
The additives of the present invention may be incorporated in the aqueous pesticide composition during the initial formulation process or may be added at any subsequent stage of storage, transportation or packaging to reduce corrosion. The additives of the present invention have the further advantage of being readily available at relatively low cost.
The use of nitrate salts, especially ammonium nitrate, as nitrogen fertilizer is long established in the agricultural industry, and the use of ammonium nitrate or other nitrogen fertilizer solutions as a tank mix carrier liquid for application of herbicides is frequently included on the label instructions for the product. However, the use of nitrate salts in nitrogen fertilizer carrier liquids involves large quantities per acre.
There are also reports in the patent literature (U.S. Pat. No. 5,658,855, US 2003104947, US 2003125211 and WO 02/19823) for use of compositions containing ammonium nitrate as application spray additives for increased herbicide activity. However, the pesticide compositions that incorporate these additives are very dilute spray mixtures that are typically prepared just prior to use by mixing components directly in the spray equipment.